The present invention relates to an angular rate sensor for an attitude controlling and navigation of mobile units including air crafts, automobiles, robots, vessels, and vehicles, for a protection from wobble of a still camera or video camera hands, and for a remote controller for remote controlling.
A monolithic type of an angular rate sensor is known as fabricated by directly bonding two quartz counterparts as single crystalline piezoelectric materials in the direction of the crystallographic axis and the thickness which create opposite polarities of piezoelectric effect and then cutting them into a tuning-fork shape. FIG. 15 is a schematic view of the arrangement of electrodes on arms of a tuning fork oscillator in the angular rate sensor. The sensor will be described below.
As shown in FIG. 15, the tuning fork oscillator 100 has arms 100a and 100b. The tuning fork oscillator 100 also has a set of electrodes 101 to 108 provided on the arms 100a and 100b substantially throughout the whole length. Each electrode is formed by sputtering or vapor depositing a layer of Cr on a base material and then sputtering or vapor depositing a layer of Au, Ag, Al, or the like on the Cr layer. A pair of driver electrodes 101 and 102 are mounted on a first main surface and a second main surface of the arm 100a, respectively. A monitor electrode 106 is mounted on the second main surface of the arm 100a. Grounding electrodes 103, 104, and 105 are mounted on outer and inner surfaces of the arm 100a and a first main surface of the arm 100b, respectively. A pair of detector electrodes 107 and 108 are mounted on inner and outer surfaces of the arm 100b, respectively.
For a piezoelectric oscillation along the main surfaces of the tuning fork oscillator 100 at a resonance frequency, the pair of the driver electrodes 101 and 102 mounted on the arm 100a are connected to an oscillator 109 and electrically driven by the oscillator 109. The amplitude of the oscillation on the tuning fork oscillator 100 developed by the oscillator circuit 109 is measured by the monitor electrode 106 mounted on the second main surface of the arm 100b. An angular rate input about the axis of the tuning fork oscillator 100 generates a Coriolis force in a direction vertical to the main surface of the arm 100b. The force develops a stress on the arm 100b, and then the stress is detected by the detector electrodes 107 and 108 piezoelectrically.
A charge generated on the monitor electrode 106 is amplified by an external circuit and transferred to an automatic gain control (AGC) circuit. Then, it is compared with a reference level signal predetermined by the AGC circuit. The circuit controls the oscillator 109 in order to maintain a constant amplitude of the oscillation of the tuning fork oscillator 100. A signal from the detector electrodes 107 and 108 is amplified by an external circuit. The signal is synchronously-detected with the oscillation of the tuning fork detected by the monitor electrode 106, so that a signal with the Coriolis force modulated by the tuning fork oscillator 100 may be demodulated. Then, the signal has an undesired frequency component cut off by a low pass filter (LPF), and is output as a sensor output.
The conventional angular rate sensor having the foregoing arrangement has the paired driver electrodes provided on the main surfaces of one of the arms. Thus, this makes the driving operation of the tuning fork oscillator electrically driven with a constant voltage be hardly improved.
The present invention is developed for solving the above drawback and the object is to provide an angular rate sensor which is improved in the efficiency of the driving operation.
In order to achieve the object of the present invention, an angular rate sensor includes a tuning fork oscillator having a first oscillator member of a single crystalline piezoelectric material composed of at least two arms and a base joining the two arms and a second oscillator member of the single crystalline piezoelectric material having a substantially identical shape to the first oscillator member. The two oscillator members are bonded directly to each other in the direction of the crystallographic axis and the thickness so that opposite polarities of a piezoelectric effect may be developed along the widthwise direction of the oscillator members. The tuning fork oscillator thus includes at least two arms and a base. The sensor further includes: first, second, third, and fourth electrodes provided on a first main surface, a second main surface, an outer surface, and an inner surface of one of the two arms of the tuning fork oscillator, respectively; a fifth electrode provided on either a first main surface or a second main surface of the other arm of the tuning fork oscillator; and sixth and seventh electrodes provided on an inner surface and an outer surface of the other arm of the tuning fork oscillator, respectively.
When the fifth electrode is provided on the first main surface, a driving voltage is applied to the second and fifth electrodes at the same polarity, and applied to the first electrode at the reverse polarity against the second and fifth electrodes.
When the fifth electrode is provided on the second main surface, a driving voltage is applied to the second and fifth electrodes at the opposite polarity to each other, and applied to the first electrode at the same polarity as the fifth electrode.
The angular rate sensor has the efficiency of a driving operation improved.